Some subsea operations require regularly liquid supply from the surface via umbilicals. At large depths long umbilicals are required, and replenishing of liquid goes slow. Liquid to be consumed is therefore usually stored on the seabed.
In various subsea operations there is a risk of improper opening or closing of valves, resulting in momentary pressure rise or pressure fall that may harm seals or other pressure sensitive components. In other situations influence of temperature on liquids inside confined spaces will make it necessary quickly to supply or remove liquid in a controlled manner in order to avoid harmful pressure variations.
Thus, there is a need for pressure stabilizing devices, preferably in the form of quick responding modulating valves that connect the area in question with a high pressure supply system or a low pressure receiving system.
In many situations it is desirable to reuse the liquid, which means that the systems must be able to return the liquid as required.
In most subsea installations electric power is available. Hence, it is appropriate to use electrically driven pumps. To reuse liquid that has been removed to prevent pressure build-up, the receiving system for that liquid must be able to receive and return it in a simple and reliable manner.
As the oil industry has been involved in larger sea depths, it has been increasingly important to find good solutions to these needs.